The present invention may be widely applicable to the production in general of an electronic device material in a semiconductor apparatus (semiconductor device), a liquid crystal apparatus (liquid crystal device) and the like, but for the sake of convenience, the present invention is described here by referring to, for example, the technique of forming a gate insulating film of a MOSFET in a semiconductor apparatus and the background art thereof.
The substrate for a semiconductor or electronic device material including silicon is subjected to various processings such as formation of an insulating film including an oxide film, film-formation by CVD or the like, and etching.
It is not an exaggeration to say that high-performance fabrication of a semiconductor device in recent years has been developed on the miniaturization technique of the device including a MOSFET. Still at present, improvement of the miniaturization technique of a MOSFET is being made with an attempt to achieve higher performance. To cope with recent demands for miniaturization and high performance of a semiconductor device, needs for an insulating film having higher performance (for example, in view of leakage current) are keenly increasing. This is because even a leakage current on a level of causing no actual problem in a conventional device having a relatively low integration degree has a possibility of consuming a large quantity of electric power in a recent miniaturized and/or high-performance device. Particularly, a low power consumption device is essential for the development of a portable electronic device in a recently started so-called ubiquitous society (information society allowing for connection to the network at any time and any place through an electronic device as the medium), and reduction of the leakage current is a very important problem.
Typically, for example, in developing a next-generation MOSFET, thinning of a gate insulating film is approaching the limit with the progress of the above-described miniaturization technique and a large problem to be solved comes out. That is, as for the process technique, the silicon oxide film (SiO2) used as a gate insulating film at present can be thinned to the extreme (on a level of one- or two-atom layer), but when the film is thinned to a thickness of 2 nm or less, there arises a problem that an exponential functional increase of leakage current is generated by the direct tunnel due to a quantum effect and the power consumption increases.
At present, the IT (information technology) market is changing from a fixed electronic device (a device to which an electric power is supplied from a wall socket) as represented by a desktop-type personal computer, a home telephone and the like to a “ubiquitous network society” allowing for connection, for example, to the network at any time and any place. Accordingly, it is considered that a mobile terminal such as cellular phone and car navigation system becomes mainstream in the near future. Such a mobile terminal is required to be a high-performance device in itself but at the same time, must be promised to have a function capable of standing long use even when driven by a small and lightweight battery, electric cell or the like which is not so much required in the fixed device. In this way, reduction in the power consumption while achieving such a high performance is very important for the mobile terminal.
Typically, when miniaturization of a high-performance silicon LSI is sought for in the process of developing, for example, a next-generation MOSFET, there arises a problem that the leakage current increases and in turn, power consumption increases. For decreasing the power consumption while seeking for the performance, it is necessary to enhance the characteristic without increasing the gate leakage current in a MOSFET.
In order to satisfy such a requirement for the realization of a high-performance MOSFET with low power consumption, various techniques (for example, use of silicon oxide nitride film (SiON) as the gate insulating film) have been proposed and one useful technique is the development of a gate insulating film using a high-k (high dielectric constant) material, that is, a material having a dielectric constant higher than that of SiO2. By using such a high-k material, the EOT (equivalent oxide thickness) which is a film thickness in terms of SiO2 can be made smaller than the physical film thickness. In other words, a film having a physically large thickness with the same EOT as SiO2 can be used and great reduction of the power consumption can be expected. At present, HfO2, Al2O3, Ta2O5, ZrO2 and the like which are a material having a dielectric constant higher than that of SiO2 come up for such a high-k material.
(Non-Patent Document 1)
M. A. Cameron and S. M. George, Thin Solid Films, 348 (1999), pp. 90-98, “ZrO2 film growth by chemical vapor deposition using zirconium tetra-tert-butoxide”
(Non-Patent Document 2)
Sadayoshi Horii, Masayuki Asai, Hironobu Miya, Kazuhiko Yamamoto and Masaaki Niwa, Extended Abstracts of the SSDM, Nagoya, 2002, pp. 172-173, “Improvement of Electrical Characteristic for High-k Dielectrics Grown by MOCVD via Cyclic Remote Plasma Oxidation”
(Non-Patent Document 3)
Katsuyuki Sekine, Yuji Saito, Masaki Hirayama and Tadahiro Ohmi, J. Vac. Sci. Technol. A 17(5), September/October 1999, pp. 3129-3133, “Silicon nitride film growth for advanced gate dielectric at low temperature employing high-density and low-energy ion bombardment”
(Non-Patent Document 4)
Takuya Sugawara, Toshio Nakanishi, Masaru Sasaki, Shigenori Ozaki and Yoshihide Tada, Extended Abstracts of Solid State Devices and Materials, 2002, pp. 714-715, “Characterization of Ultra Thin Oxynitride Formed by Radical Nitridation with Slot Plane Antenna Plasma”
However, in the case where an insulating film using a high-k material expected to ensure such excellent characteristic is formed in practice by a CVD method (chemical vapor deposition) or the like, the film formation is performed at a low temperature so as to enhance the in-plane uniformity and therefore, the obtained film allows for the presence of a large number of non-bonded bonds (dangling bond), weak Si—O bonds (suboxide), carbons contained in the raw material for film formation, or the like and can hardly have good characteristic (Reference Document [1]). Accordingly, it is very important for practically using a high-k material film to eliminate these causes giving rise to deterioration of the film quality. As for the means to solve this problem, an attempt of applying a modification treatment by thermal annealing to the insulating film, thereby improving the film characteristic, is being made (Reference Document [1]). However, the modification treatment by thermal annealing is associated with a problem such as deterioration of the characteristic resulting from crystallization of the insulating film due to a high-temperature process, or increase in the electrical film thickness (lowering of effective dielectric constant) due to oxidation of silicon at the insulating film-silicon interface.
As for the method of solving these associated problems in the modification treatment by thermal annealing, a modification treatment of an insulating film by a plasma capable of effecting a modification treatment at a substrate temperature of about 400° C. has been proposed (Reference Document [2]). By use of this modification treatment of an insulting film by a plasma, the weak bond of a suboxide may be repaired at a low temperature to form a strong Si—O bond, or carbon in the film may be burned, so that good electrical characteristic can be obtained. However, the plasma forming method reported at present has a problem such as plasma damage due to high electron temperature or difficulty in large-area formation (Non-Patent Documents 1 and 2).
In order to solve such a problem, a plasma forming method using a plane antenna and microwave has been recently proposed as a plasma treating method for the formation of a gate insulating film. This is a method where a rare gas such as He, Ne, Ar, Kr and Xe is supplied together with an oxygen- or nitrogen-containing gas from a ring-like shower plate provided above a substrate to be treated to a space between the plate to be treated and the shower plate, and microwave is irradiated from the behind of a plane antenna having a slot (slot plane antenna (SPA)) provided above the shower plate, whereby microwave is introduced through the antenna and the rare gas is plasma-excited by using the microwave in the space. A technique of forming an oxygen radical* or a nitrogen radical N* by using this plasma, and oxidizing or nitriding the surface of a silicon substrate has been proposed. The plasma formed by this method has a high electron density and therefore, a radical is produced in a large amount even at a low substrate processing temperature. Also, the electron temperature is low and therefore, the plasma damage brought about as a problem in other plasma forming methods is low. Furthermore, it is reported that since microwave propagated through a plane antenna uniformly forms a plasma in a large area, an excellent effect is provided also in view of application to a large-area substrate such as 300-mm wafer or substrate for a large TFT display device (Non-Patent Documents 3 and 4).
By using such a technique, a radical can be formed in a large amount even when the surface of an electronic device substrate is at a low substrate temperature of 400° C. or less. Other than the application to formation of an oxide film or oxynitride film, this technique is promising also for use in the modification treatment of an insulating film. In practice, studies related to the modification of an insulating film by using this plasma are being made, but a sufficiently high modification effect is not yet attained only by modification using the plasma.